David J. Rose

Highly Ionized Hollow Cathode Discharge

A hollow cathode discharge (HCD) is described that produces a highly ionized steady‐state plasma (ne≈1013−1014/cm3) at a temperature 1–10 eV, in a volume as large as 104 cm3, with background neutral gas density ≈1013/cm3. The HCD is generated by the prescription: gas flow (H2, He, A, or N2) 0.05–2 cc STP/sec through a refractory metal hollow cathode tube into a vacuum; any anode; 20–200 V dc applied. An axial induction 100–1000 G is used to collimate the discharge and to aid in starting by rf excitation. The HCD runs from the cathode interior, deep enough that p0d≈1 cm×mm Hg. Current range is 2.0–300 A. Various electrode configurations and a wide range of operating parameters have been studied. The external plasma density and temperature were measured by Langmuir probes. A discussion is given of the confinement mechanism and of the energy balance, both in the external plasma and in the region of the cathode itself.

Disposal of Nuclear Wastes At an increased but still modest cost, more options can be explored and the outlook can be improved

For the present and the foreseeable future the following options appear to be either usable or worth further exploration: mausolea; disposal in mines of various sorts, and perhaps in ice; in situ melt; and further chemical separations. The options are interdependent. It is too early to assess disposal in space, and disposal in the oceans remains unsafe for lack of adequate knowledge. Table 3 is a summary of the main ideas for which we have worked out (sometimes uncertain) costs. For the short term, ultimate disposal in deep mines is the best-developed plan. However, the related concept of in situ melt has significant advantages and should be realistically appraised. Further chemical separation with subsequent recycling of the actinides in a LMFBR should be investigated and implemented, for it would be universally beneficial; on the other hand, additional removal of strontium and cesium does not seem attractive. Thus, for the near future we make the following recommendations: 1) Provide temporary storage facilities to ensure that the projected commercial high-level wastes do not become a public hazard. The AEC adopts this view, and has stated an intention to construct such facilities. But because of the capriciousness of man and nature, a workable ultimate disposal scheme must be developed soon. 2) Fund other ultimate disposal schemes at the same rate as the salt mine project—say

Methods of Measuring the Properties of Ionized Gases at High Frequencies. III. Measurement of Discharge Admittance and Electron Density

1 million a year or more—to sharpen the technological issues, so that a decision can be reached in the next few years. The schemes should include (i) in situ melt, and the variation with a central repository; (ii) burial in mines other than salt mines (including Antarctic rocks and permanent ice); (iii) further chemical separation of actinides and recycling actinides in a LMFBR. 3) Maintain liaison with the developing space shuttle technology to insure that no opportunity is lost. The AEC has a commitment to hold safety foremost in its waste management program, but budget considerations and management priorities have downgraded the program. Past funding levels and management emphasis have yet to produce, after a decade and a half, one operational long-term storage facility—a sign of both commendable caution and inadequate work. If nuclear power is to resolve our energy needs in the coming decades, its benefits should not be delayed for lack of a viable management program for high-level wastes.

Plasma Diagnostics by Thomson Scattering of a Laser Beam

Experimental methods are given for determining the complex admittance and electron density of gas discharges by the use of microwave techniques. Applications are discussed where the discharge is contained in either high or low Q resonant cavities.

Methods of Measuring the Properties of Ionized Gases at High Frequencies. I. Measurements of Q

The use of Thomson scattering of a laser beam as a diagnostic technique for laboratory plasmas is discussed. Several potential sources of difficulty in the use of this technique are investigated. Included are simple signal‐to‐noise considerations based upon photon counting statistics and noise due to plasma radiation, Rayleigh or Raman scattering from neutral particles in the plasma, and scattering from walls, apertures, etc. in the apparatus. Also discussed are other effects which may affect the state of the plasma being measured, namely, free‐free absorption which leads to electron heating and free‐bound absorption or photo‐ionization which can produce additional electrons. Experimental determinations of electron density and temperature in a steady‐state hollow‐cathode arc plasma, by Thomson scattering of a ruby laser beam, are reported and discussed. These measurements refer primarily to argon plasmas over an electron density range 1013–1014 cm−3 and electron temperature range 3–8 eV. Essential agreeme...

Plasma Diagnostics using Lasers: Relations between Scattered Spectrum and Electron‐Velocity Distribution

Experimental methods are given for determining the Q of both high and low Q resonant cavities at microwave frequencies. The emphasis is placed on the practical measurements necessary in determining the properties of ionized gases in the 3‐ and 10‐centimeter wavelength range.

Methods of Measuring the Properties of Ionized Gases at High Frequencies. II. Measurement of Electric Field

Laser light scattered from plasma electrons can be used to determine the electron density and velocity distribution. The process is classical Thomson scattering, and the scattered spectrum is constructed of the Doppler shifts of the electrons. The spectrum I(k), which appears at all angles and over a range of wave‐numbers, is uniquely related to the electron velocity distribution f(v). Either can be obtained from the other, and we derive the expressions I(k) = Lf(v) and f(v) = L−1I(k) relativistically correctly. We also discuss the amount of information about f(v) obtainable from a simple measurement of the scattered spectrum. The electron density and mean speed can be measured easily; more subtle features depend upon accurate observation of the low‐intensity wings of the spectrum.

Electron Density in Mixed Gas Plasmas Generated by Fission Fragments

Experimental methods are given for determining the electric field within resonant cavities in the microwave region. Methods are discussed of calculating the electric field in both simple and complex structures used in gas discharge studies.

ION TEMPERATURE, CHARGE EXCHANGE, AND COULOMB COLLISIONS IN AN ARGON PLASMA COLUMN.

Studies of electron density are reported for a quiescent neon‐argon gas plasma generated by fission fragments in the core of a nuclear reactor. Reaction kinetic equations for the various ionic and excited species are solved self‐consistently with electron‐energy balance equations to yield values of electron density and temperature. It is shown that for containers of diffusion length of about 1.6 mm or greater, there exists a maximum value of electron density at a total gas pressure p≈90 Torr and [Ar]/[Ne]≈10−4; the dominant ion in this case is the atomic Ar+ ion. At low values of neutron flux (∼1010 cm−2 sec−1) and electron density (∼1010 cm−3), the electron temperature is computed to be at or near the gas temperature, but at high values of neutron flux (∼1013 cm−2 sec−1) and electron density (∼1012 cm−3), the electron temperature is higher than the gas temperature by an important amount (∼600°K). Inpile measurements of electron density using microwave techniques are in very good agreement with the theore...

Combined Anode‐Cathode Feed of a Hollow‐Cathode Arc

Ion temperatures in a highly ionized argon plasma column have been measured with a Fabry‐Perot interferometer. Plasma‐column conditions were altered over a range of parameters from 10% to 70% ionized, electron temperature Te=2–10 eV, and magnetic field 1400–2800 G. In general, Ti is about one‐tenth Te, determined by the balance between electron heating and charge‐exchange cooling. The measured values of Ti agree fairly well with those calculated, using accepted values of Coulomb collision and charge‐exchange cross sections. Alternately, the present data are processed to derive approximate values of the charge‐exchange cross section to neutral argon as a function of Ar+ ion energy in the range 0.1–1.0 eV. It can also be concluded that the theoretical rate for electron‐ion energy relaxation is not seriously in error.